The present invention relates generally to structures for carrying rotary magnetic heads (hereinafter referred to as rotary magnetic head carrier(s)) such as rotary guide drums, rotary discs, and the like, which carriers hold rotary magnetic heads mounted thereon and rotate unitarily therewith. More particularly, the invention relates to a rotary magnetic head carrier having improved shapes of the outer edge parts on the opposite sides of each recess or cutout in which the head tip of a rotary magnetic head is fitted.
In general, in an apparatus for recording and/or reproducing a video signal on and/or from a magnetic tape by means of rotary magnetic heads (hereinafter referred to as a "VTR" apparatus), the above mentioned magnetic heads are mounted on and held or carried by a rotary structure such as a rotary guide drum or a rotary disc, rotating between a pair of fixed guide drums, and rotate unitarily with the rotary structure. A magnetic head assembly of this kind, in general, comprises a support plate to be mounted on the rotary structure constituting a rotary magnetic head carrier and a head tip comprising a core mounted on the outer end of the support plate and a coil wound around the core. The head tip is secured to the support plate with an adhesive, for example. Recesses or cutouts are provided in the rotary structure. A head tip and the adhesive, in a swollen state, are fitted in each recess when the support plate of the magnetic head is mounted on the rotary structure.
The recesses in the rotary structure desirably facilitate the forming operation. Small size openings of each recess, at the outer peripheral surface of the rotary structure, are fulfilled as requirements. The small size openings are desirable so that the gaps on both sides of the head tip at the outer peripheral surface of the rotary structure may be narrow.
Accordingly, a method of forming the recesses while satisfying the above stated conditions has been developed. This method comprises bringing a rotating cutter of a rod shape into contact with the rotary structure at a position such that the center of rotation of the cutter is at a distance which is less than the radius of rotation of the cutter from the outer peripheral surface of the rotary stucture and machining one end surface of the rotary structure by a specific dimension. By this method, a recess is formed with a shape which is a circle with a part thereof cut away and thus has a small opening at the outer peripheral part of the rotary structure. The recess becomes wider at its inner portion.
At the time of this machining to form the recess, the opposite side parts of the recess become very thin at the outer peripheral part of the rotary structure. Minute edge projections such as burrs are produced. If these minute projections are not removed, they will scratch or peel off the magnetic layer of the magnetic tape when the rotary structure rotates to cause the magnetic heads to scan the magnetic tape. When the magnetic tape is damaged in this manner, dropouts will occur in the reproduced signals. Furthermore, the magnetic particles thus peeled off adhere to the magnetic tape and magnetic heads, and this also is a cause of dropout. As a consequence, there are undesirable occurrences which seriously impair the recorded and reproduced signal.
Accordingly, buffing has been carried out to remove the above mentioned minute projections. However, in order to avoid, as much as possible, deforming parts of the outer peripheral surface of the rotary structure other than the recesses and to retain as much as possible the true circularity of the rotary structure, it is necessary to bring the rotating buffing tool into contact therewith in an oblique direction, relative to the outer peripheral surface and end surface of the rotary structure, thereby to remove the minute projections by buffing. However, by this method, even parts which do not require buffing in the vicinity of the opening of the recess at the outer peripheral surface of the rotary structure are polished into an arcuate shape, and the true circularity of the outer peripheral surface is impaired. Furthermore, it is difficult to carry out this buffing work automatically; therefore, it is usually carried out manually. For this reason, there is much deviation in this buffing work, and the accuracy is poor. In addition, there are other problems such as the need for skilled labor in this work.
Furthermore, in the case where materials such as chromium oxide are used in the polishing process, there are further problems such as the necessity of installing processing equipment for preventing environmental pollution and high production cost.